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Backup Route means?


"For protocols that don't have their own routing information tables, such as IGRP, the first method is used. Every time IGRP receives an update about a route, it attempts to install the updated information in the routing table. If there's already a route to this same destination in the routing table, the installation attempt fails.

For protocols that have their own database of routing information, such as EIGRP, IS-IS, OSPF, BGP, and RIP, a backup route is registered when the initial attempt to install the route fails. If the route installed in the routing table fails for some reason, the routing tabel maintenance process calls each routing protocol process that has registered a backup route, and asks them to reinstall the route in the routing table. If there are multiple protocols with registered backup routes, the preferred route is chosen based on administrative distance."

Above paragraph, What is the meaning of ' registered backup route' .

When Two routers have multiple protocols(RIP and OSPF), there are OSPF route on routing table which is chosen by AD value.

Then, Rip has the routes on its database as a registered backup route?

If Not so, what is the problem?

As my testing result, I didn't find routes registered on rip database by 'show ip rip database'.

If 'show ip rip database' command cannot show the whole database of rip, then ho can I indicate that the route registered to rip databse as a 'registered backup route'?


Re: Backup Route means?

Actually RIP dont have the concept of backup registered route. When a route goes down, triggered updates will be sent and if before the holdown timer expires , a new route is discovered with a better metric, that route will be added to the routing table once the holddown timer expires.

Backup routes are mainly intended to reduce the convergence time. In the case of EiGRP, since it is not having any periodic updates, it will be better to have a backup route so that as soon as the primary route goes down , the traffic can pass through using the back up route. Otherwise it will take a long time to undergo DUAL algorithm again. I think the document you are referring might be having some mistake.